Skip to main content

AngularJS - Resolving data services before instantiating the Controller and Template

I have been working on an Angular application for sometime now and I have started to like this approach to client-side development. It's a different approach when compared to developing applications using Backbone and Require. I was looking at routing in Angular and came across the 'resolve' property which can be used to resolve services before instantiating the Controller and it's corresponding template i.e. the domain models that are required for the View components are resolved first.

Look at a scenario where you are using a Search service to get a collection of objects that contain the search string. You can specify the route which will display the search results. When only the template and controller properties are specified, both are instantiated and the ng-view is updated with the specified template. The controller  would specify dependency on the SearchService,use this service to query the back-end and then update one of the $scope variables with the response data.

While the SearchService is fetching results, you would see that the template being displayed inside the ng-view container with template variables and the same getting updated when the service returns data. This is not ideal; the search results should be available before you load the controller; and the template should display data instead of showing template variables. The 'resolve' property in the $routeProvider mentions a set of promises that should be resolved before instantiating the controller and the template. Only when all the promises are resolved, the controller and the template are instantiated. Also the promise reference is injected into the controller as a dependency. Using this promise one can directly update the values in the template instead of sending a request to the Search service.

Here's the code for the routeProvider :

Here the route '/search/:searchString', specifies the 'resolve' object which includes a promise - 'searchResults'. It queries the searchService and returns a promise. When the service is resolved the Controller - 'searchController' and the template - 'partials/search.html' are instantiated. The Controller gets the promise object:

Notice that the promise - 'searchResults' is injected into the Controller and it contains the response data. This can then be used to render the template.
Labels:

Comments

  1. VanTanevJuly 15, 2014 at 5:52 PM

    This is something I'm not familiar with - if searchService.getSearchResults returns a promise, and that promise is resolved before being injected (as per the resolve contract), why is the data with which the promise was resolved under .data? Or is this your model, the resolved value is {data:[results]}?

    ReplyDelete
  2. Sagar GanatraJuly 15, 2014 at 8:54 PM

    the http response object constructed contains four properties - 'data' (response data), 'config', 'status', 'statusText' and 'headers'. In this case to refer to the response data, response.data should be used. Alternatively you can write a httpInterceptor and return response.data as response.

    ReplyDelete
  3. VanTanevJuly 15, 2014 at 9:30 PM

    Ah, so you're resolving the promise with the response object from $http? I would usually have a specific property on my response, for example {results: []}, and then resolve with "response.data.results". Most times, I even like to verify the `results` key exists, and will reject the promise if it doesn't (regardless of response status code), just to be extra safe that the promise was resolved with the data I actually want.

    ReplyDelete

Post a Comment

Popular posts from this blog

Custom validation messages for HTML5 Input elements using the constraint validation API

HTML5 has introduced several input types such as EMAIL, URL, RANGE, SEARCH, DATE, TIME, etc,. Most of the modern browsers have implemented them and are ready to be used in a HTML document. Another exciting feature introduced in HTML5 is the form validation. Instead of writing JavaScript to validate users input, browsers can now validate it and show an appropriate message if the validation fails. The validation message is shown in line with the field for which the validation has failed. The default error message is shown when the validation fails. In this post I'll explain how these error messages can be changed.
12 comments
Read more

De-obfuscating javascript code in Chrome Developer Tools

I had blogged about JavaScript debugging with Chrome Developer Tools some time back, wherein I have explained how these developer tools can help in debugging javascript code. Today Google Chrome 12 was released and my Chrome browser was updated to this version. As with every release, there have been some improvements made on performance, usability etc,. One feature that stood out for me is the ability to De-obfuscate the javascript code.

What is Minification?

Minification is the process of removing unnecessary characters such as white spaces, comments, new lines from the source code. These otherwise would be added to make the code more readable. Minifying the source code helps in reducing the file size and thereby reducing the time taken to download the file. This is the reason why most of the popular javascript libraries such as jQuery are minified. A minified jQuery file is of 31 KB in size where as an uncompressed one is about 229 KB. Unfortunately, debugging minified javascript file…
15 comments
Read more

Adding beforeRender and afterRender functions to a Backbone View

I was working on a Backbone application that updated the DOM when a response was received from the server. In a Backbone View, the initialize method would perform some operations and then call the render method to update the view. This worked fine, however there was scenario where in I wanted to perform some tasks before and after rendering the view. This can be considered as firing an event before and after the function had completed its execution. I found a very simple way to do this with Underscore's wrap method.
2 comments
Read more